MyQubit Amplex Red Cholesterol Assay

Transcription

1 MyQubit Amplex Red Cholesterol Assay Introduction The MyQubit Amplex Red Cholesterol Assay for use with the Qubit 2.0 Fluorometer, which is available for downloading from allows easy and accurate quantification of cholesterol using the Amplex Red Cholesterol Assay Kit (Cat. no. A12216) and the Amplex Red/UltraRed Stop Reagent (Cat. no. A33855). The MyQubit Amplex Red Cholesterol Assay file can be downloaded from our website and permanently uploaded to your Qubit 2.0 Fluorometer following the guidelines described below. Because a large portion of cholesterol in blood is in the form of cholesteryl esters, the MyQubit Amplex Red Cholesterol Assay uses an enzyme-coupled reaction that detects both free cholesterol and cholesteryl esters. Cholesteryl esters are hydrolyzed by cholesterol esterase into cholesterol, which is then oxidized by cholesterol oxidase to yield H 2 O 2 and a corresponding ketone product. The H 2 O 2 is then detected using 10-acetyl- 3,7-dihydroxyphenoxazine (Amplex Red reagent), a highly sensitive and stable probe for H 2 O 2. 1 In the presence of horseradish peroxidase (HRP), Amplex Red reagent reacts with H 2 O 2 with in a 1:1 stoichiometry to produce highly fluorescent resorufin. 1,2 Because resorufin has a fluorescence emission maximum of approximately 585 nm, there is little interference from autofluorescence in most biological samples. The MyQubit Amplex Red Cholesterol assay can detect concentrations of 200 nm 20 μm in the assay tube (Figure 1) and can accurately measure the cholesterol content in the equivalent of 0.01 μl of human serum. By performing the reactions in the presence and absence of cholesterol esterase, the assay is also potentially useful for determining the fraction of cholesterol that is in the form of cholesteryl esters within a sample. Figure 1 (A) The plot showing the line corresponding to the curve-fitting algorithm (a Modified Hill plot) used to calculate concentration in the MyQubit Amplex Red Cholesterol Assay. For reference, the positions of the standards and a set of data points from an actual experiment are shown superimposed onto the line, demonstrating that the curve-fitting algorithm gives accurate values for quantitation. (B) The assay has the same look and feel of the existing Qubit assays. A B Relative fluorescence Curve-Fitting Algorithm Standards Raw Data [Cholesterol] (µm) MAN MP99000 Revision: 1.0

2 In addition to the MyQubit Amplex Red Cholesterol Assay for quantifying cholesterol, the MyQubit firmware allows you to create other assays for your Qubit 2.0 Fluorometer. All new Qubit 2.0 instruments are pre-loaded with the MyQubit firmware, which can also be downloaded from for installation into existing instruments. Using the MyQubit firmware, additional assays can be created based on existing Life Technologies reagents and assays or completely novel ideas. Since the instrument is operated by simple commands, creating additional applications can be as straightforward as matching spectral compatibility with the LEDs and emission filters. Detailed instructions and templates for creating new MyQubit assays are also provided on the Qubit website ( Before You Begin Firmware Requirements Your Qubit 2.0 Fluorometer must have V3.10 firmware or later installed for you to be able to upload new assays using the MyQubit function. Before proceeding, make sure that your Qubit 2.0 Fluorometer has been upgraded to V3.10 firmware or later. Materials Required Amplex Red Cholesterol Assay Kit (Cat. no. A12216)* Amplex Red/UltraRed Stop Reagent (Cat. no. A33855)** Qubit 2.0 Fluorometer (Cat. no. Q32866) MyQubit Amplex Red Cholesterol assay file (Amplex Cholesterol.qbt), available for downloading at USB drive clear of other.qbt files Qubit Assay Tubes (Cat. no. Q32856) or Axygen PCR-05-C tubes (VWR part no ) Ethanol and E-pure H 2 O for reconstituting Amplex Red/UltraRed Stop Reagent Plastic tubes for preparing buffers and dilutions of standards/samples. * Each Amplex Red Cholesterol Assay Kit provides sufficient reagents for 250 assays using the Qubit 2.0 Fluorometer and the protocol described below. ** Each vial of Amplex Red/UltraRed Stop Reagent provides sufficient reagent to terminate 50 assays using the Qubit 2.0 Fluorometer and the protocol described below (Cat. no. A33855 includes 5 vials). Downloading the.qbt File from the Web Download the MyQubit Amplex Red Cholesterol assay file (Amplex Cholesterol.qbt) from and save it directly to your PC. Then, transfer the file from your computer to the root directory of your USB drive. Ensure that you only have a single.qbt file on your USB drive before uploading it to the Qubit 2.0 Fluorometer. Note: Downloading a.qbt file from the web directly to your USB drive may result in unexpected behavior. MyQubit Amplex Red Cholesterol Assay 2

3 Uploading the.qbt File to the Qubit 2.0 Fluorometer 1.1 Make sure there is only one.qbt file on your USB drive. 1.2 With your Qubit 2.0 Fluorometer unplugged, insert the USB drive containing the MyQubit Amplex Red Cholesterol assay file (Amplex Cholesterol.qbt) into the USB port on the instrument. 1.3 Plug the Qubit 2.0 Fluorometer back in to power it on. The instrument will display the following message: Amplex Cholesterol.qbt file detected. Do you wish to upload? Click Yes to proceed with the upload, which will take ~2 seconds. 1.4 Once the upload is complete, you will be directed to a new Home Screen displaying a new button called Chol, which indicates that the cholesterol assay is permanently uploaded to the instrument (Figure 2). You do not need the USB drive to access the assay. Functionality of the pre-existing assays is not affected in any way. Figure 2 Upload of the MyQubit Amplex Red Cholesterol assay. The Qubit 2.0 Fluorometer will recognize the Amplex Cholesterol.qbt file and guide you through the upload process. Material Storage and Handling Upon receipt, the Amplex Red Cholesterol Assay Kit should be stored frozen at 20 C, protected from light. When stored properly, the kit components are stable for at least six months. Allow the reagents to warm to room temperature before opening the vials. The Amplex Red reagent is somewhat air sensitive. Once a vial of Amplex Red reagent is opened, the reagent should be used promptly. Protect the Amplex Red reagent from light. Store Amplex Red/UltraRed Stop Reagent refrigerated at 2 8 C until required for use. If frozen, avoid freeze-thaw cycles. Desiccation is recommended but not essential. Refer to the detailed product information provided with the materials for additional storage and handling information, including disposal. MyQubit Amplex Red Cholesterol Assay 3

4 Critical Assay Parameters Incubation Time The MyQubit Amplex Red Cholesterol assay for use with the Qubit 2.0 Fluorometer was optimized using Amplex Red/UltraRed Stop Reagent (Cat. no. A33855). This reagent provides a means to terminate the fluorescence signal-generating reaction in the enzymatic assay. Once the stop reagent has been added (after 15 minutes), fluorescence signal remains stable for at least 3 hours (i.e., sample reads remain within 10% average deviation from the expected value using the same standard calibration). This enables the reading of multiple user samples during this time frame without requiring a new calibration. Samples that are read more than 3 hours after calibration may exhibit increased deviation from the actual concentration values. Preparing the Amplex Red/ UltraRed Stop Reagent Reconstitute one vial of Amplex Red/UltraRed Stop Reagent by adding 1.45 ml of ethanol and vortex or agitate briefly. Transfer 1.25 ml of this solution to a vial and dilute with 1.25 ml of E-pure H 2 O, giving a total of 2.5 ml of stop solution. This amount is sufficient to stop 50 assays of 200 μl each, based on the protocol described below. After reconstitution, the stop reagent is stable for approximately one month when stored at 2 8 C, protected from light. The appearance of amber coloration is indicative of decomposition. Calibrating the Qubit 2.0 Fluorometer For each assay, you have the choice to run a new calibration or to use the values from the previous calibration. As you first start using the instrument, perform a new calibration each time. As you become familiar with the assays, the instrument, your pipetting accuracy, and significant temperature fluctuations within your laboratory, determine the level of comfort you have using the calibration data stored from the last time the assay was calibrated. Remember that after the addition of the Amplex Red/ UltraRed Stop Reagent, the fluorescence signal in the tubes containing standards and the samples is stable for at least 3 hours when stored at room temperature. For best results, perform a new calibration each time a new working solution is prepared. Calculating the Concentration of Your Sample The Qubit 2.0 Fluorometer gives values for the MyQubit Amplex Red Cholesterol assay in μm. This value corresponds to the concentration after your sample was diluted into the assay tube. To calculate the concentration of your starting sample, use the following equation: Concentration of your sample = QF value 240 x where QF value is the value given by the Qubit 2.0 Fluorometer, and x is the volume of sample in microliters added to the assay tube. This equation generates a result with the same units as the value given by the Qubit 2.0 Fluorometer in the assay tube. Because the MyQubit Amplex Red Cholesterol Assay gives concentrations in μm, the result of the equation above will be in μm. MyQubit Amplex Red Cholesterol Assay 4

5 Dilution Calculator The Dilution Calculator function will not be useful when using the MyQubit Amplex Red Cholesterol Assay on the Qubit 2.0 Fluorometer. The Dilution Calculator function was designed to accommodate sample dilutions of 1 20 μl in a final assay volume of 200 μl, based on the protocols for the existing assays for DNA, RNA, and protein quantification; it is therefore not relevant for the dilution schemes used here. Experimental Procedure Preparing Buffers and Reagents Prepare all kit reagents (i.e., buffers, stock and working solutions) according to the instructions provided with the Amplex Red Cholesterol Assay Kit. Performing the MyQubit Amplex Red Cholesterol Assay The protocol below describes the MyQubit Amplex Red Cholesterol assay in a total volume of 240 μl per microplate well including the Amplex Red/UltraRed Stop Reagent (see Table 1). The final concentrations of assay standards and samples have been adjusted for the additional volume based on the dilution scheme outlined in the protocol below. The volumes recommended here are sufficient for 250 assays. Table 1 Volume of reagents used in the MyQubit Amplex Red Cholesterol assay Standard Assay Tube User Sample Assay Tube Volume of Working Solution (from Step 2.4) 100 μl 100 μl Volume of Standard 100 μl Volume of User Sample 100 μl Volume of Stop Reagent 40 μl 40 μl Total volume in each Assay Tube 240 μl 240 μl Note: The instructions provided with the Amplex Red Cholesterol Assay Kit may be used for reagent preparation. However, given the difference in reagent volumes used in the MyQubit cholesterol assay and the assay kit, the following procedure should be used in place of the Cholesterol Assay protocol (Section 2) provided with the Amplex Red Cholesterol Assay Kit. Refer to the Qubit 2.0 Fluorometer User Guide, available for for downloading at for detailed instructions on instrument use. 2.1 Set up two Assay Tubes for the standards and one for each user sample. Use only thin walled, clear 0.5 ml PCR tubes. Acceptable tubes include Qubit assay tubes (set of 500, Cat. no. Q32856) or Axygen PCR-05-C tubes (VWR, part no ). 2.2 Prepare a dilution of the cholesterol reference standard for use as Standard 2 in calibration of the Qubit assay by adding 4.6 μl of the cholesterol reference standard to 1.0 ml of 1X Reaction Buffer. This 1 ml of 24 μm cholesterol solution is sufficient to perform 10 standard calibrations. Store any unused portion of standard at < 20 C. Note: The cholesterol reference standard comes as a 2 mg/ml stock solution (5.17 mm), and calibration requires a final concentration of 10 μm cholesterol in the assay well. Since the cholesterol concentration will be 2.4-fold lower in the final reaction volume (after addition of the Amplex Red/UltraRed Stop Reagent), the cholesterol reference standard is diluted to 24 μm in 1X Reaction Buffer. MyQubit Amplex Red Cholesterol Assay 5

6 2.3 Prepare calibration standards by adding 100 μl of 1X Reaction Buffer to one assay tube (Standard 1) and 100 μl of 24 μm cholesterol solution to another assay tube (Standard 2). 2.3 Dilute your cholesterol-containing samples in 1X Reaction buffer. A volume of 100 μl will be used for each reaction. You may wish to prepare several different dilutions for each sample. Add 100 μl of each sample to a separate assay tube. 2.4 Prepare a working solution of 300 μm Amplex Red reagent containing 2 U/mL HRP, 2 U/mL cholesterol oxidase, and 0.2 U/mL cholesterol esterase by adding 15 μl of Amplex Red reagent stock solution, 10 μl of HRP stock solution, 10 μl of cholesterol oxidase stock solution, and 1 μl of cholesterol esterase stock solution to 0.96 ml of 1X Reaction Buffer. This 1 ml volume is sufficient for ~10 assays. 2.5 Start the reactions by adding 100 μl of the Amplex Red reagent/hrp/cholesterol oxidase/cholesterol esterase working solution to each assay tube containing standard and sample. Try to add the working solution to all assay tubes at the same time; if possible, use a multi-channel or repeat pipettor. 2.6 While the standard and sample reactions are incubating at room temperature, protected from light, reconstitute the Amplex Red/UltraRed Stop Reagent according to the instructions provided product (also described above under Critical Assay Parameters, page 4). 2.7 After incubating the reactions for 15 minutes at room temperature, protected from light, add 40 μl of prepared Amplex Red/UltraRed Stop Reagent to each assay tube, standards and sample(s). 2.8 Vortex all of the tubes for 2 3 seconds. 2.9 Calibrate the assay and read samples by selecting Chol from the Home Screen and following the on-screen instructions, similar to the operation of the existing assays. For detailed instructions, refer to the Qubit 2.0 Fluorometer user guide, available for downloading at The concentration reported by the instrument is the concentration of cholesterol in the actual assay tube. Note: The Dilution Calculator function will not be useful when using the MyQubit Amplex Red Cholesterol Assay on the Qubit 2.0 Fluorometer. The Dilution Calculator function was designed to accommodate sample dilutions of 1 20 μl in a final assay volume of 200 μl, based on the protocols for the existing assays for DNA, RNA, and protein quantification; it is therefore not relevant for the dilution schemes used here. To calculate the concentration of your starting sample, use the following formula: Concentration of your sample = QF value 240 x where QF value is the value given by the Qubit 2.0 Fluorometer, and x is the volume of sample in microliters added to the assay tube. MyQubit Amplex Red Cholesterol Assay 6

7 Appendix 1. You may omit the use of the Amplex Red/UltraRed Stop Reagent, if desired. Doing so allows the enzymatic reaction to continue longer, which may be useful for samples containing low concentrations of cholesterol. Samples such as this may require longer incubation times to generate fluorescence signal sufficient to provide reliable quantification. However, the parameters used in the.qbt file for the MyQubit Amplex Red Cholesterol assay have not been validated in the absence of Amplex Red/ UltraRed Stop Reagent. The shape of the standard curve used in calibration will be altered with variations in incubation time. In addition, since the Qubit 2.0 Fluorometer is designed for low-to-mid throughput use and is equipped to read only a single sample at a time, variation in incubation time could potentially result in diminished accuracy. Therefore, we recommend customizing the parameters in the Amplex Cholesterol.qbt file to optimally suit your needs. For detailed instructions on how to create a custom assay using MyQubit, refer to Conversely, you may use Qubit Raw mode to collect raw fluorescence data over multiple time points to measure the kinetics of the reaction. 2. The Amplex Red Cholesterol Assay Kit has also been shown to be compatible with Amplex UltraRed reagent. The Amplex UltraRed reagent (Cat. no. A36006) provides all of the same performance characteristic of Amplex Red while displaying improved stability over a larger ph range and, in some cases, increased sensitivity. The same assay protocol and reagent dilutions may be used with Amplex UltraRed reagent. However, for best results, we recommend optimizing the parameters in the Amplex Cholesterol.qbt file for use with Amplex UltraRed reagent. For detailed instructions on how to create a custom assay using MyQubit, refer to References 1. Anal Biochem 253, 162 (1997); 2. J Immunol Methods 202, 133 (1997). Product List Current prices may be obtained from our website or from our Customer Service Department. Cat. no. Product Name Unit Size Q32866 Qubit 2.0 Fluorometer each A12216 Amplex Red Cholesterol Assay Kit kit A33855 Amplex Red/UltraRed Stop Reagent set Q32856 Qubit Assay Tubes set MyQubit Amplex Red Cholesterol Assay 7

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